Internal fixation of femoral fractures is one of the most common orthopedic surgical procedures. Many different types of femoral fractures are encountered in practice, including fractures in the femoral neck, intertrochanteric, mid-shaft and distal condylar regions. The femoral bone will sometimes fracture cleanly into two large fragments along a well-defined fracture line, and on other occasions fracture into many smaller fragments. Often, more than one type of fracture will exist concurrently in different regions of the femur of an injured patient.
A wide variety of implants have been developed over the years for use in the internal fixation of femoral fractures. Although numerous excellent design achievements have been realized, several general problem areas remain. First, almost all of the currently available implants have a highly specialized application limited to only one specific anatomical location in the femur. Thus, a hospital must maintain at great expense a very large and variegated inventory of different implants to handle all expected contingencies. These implants are generally not compatible, i.e. they cannot be interconnected together in case of a complicated fracture pattern extending into different anatomical regions of the femur. Second, each implant has its own peculiar attributes and deficiencies, and the use of many of the known implants involves the use of a surgical technique that is unique to that implant and sometimes complicated and difficult as well. Consequently, the opportunities for improper implant selection and surgeon error during implantation are inevitably increased. Finally, tissue reactions with implants made of stainless steel and certain other surgical implant alloys tend to reduce the useful lifetime of the implants and require premature removal from the patient's body.
One very commonly utilized femoral internal fixation device is an elongated implant (nail, screw, pin, etc.) adapted to be positioned along the longitudinal axis of the femoral neck with its leading end portion in the femoral head so as to stabilize a fracture of the femoral neck. The elongated implant may be implanted by itself or connected to another implant such as a side plate or intramedullary rod. The leading end portion of the implant typically includes means to positively grip the femoral head bone (external threads, expanding arms, etc.), but the inclusion of such gripping means can introduce several significant problems. First, implants with sharp edges on the leading end portion, such as the externally threaded implants, exhibit a tendency to migrate proximally towards the hip joint bearing surface after implantation. Such proximal migration under physiological loading, which is also referred to as femoral head cut-out, can lead to significant damage to the adjacent hip joint. Also, the externally threaded implants can generate large stress concentrations in the vicinal bone during implantation which can lead to stripping of the threads formed in the bone and thus obviously a weakened grip. The movable arms of known expanding arm devices are usually free at one end and attached at the other end to the main body of the leading end portion of the implant. As a result, all fatigue loading is concentrated at the attached ends of the arms and undesirably large bending moments are realized at the points of attachment.
As stated above, known elongated implants used to stabilize fractures of the femoral neck are often connected in use to a side plate which in turn is secured to the outer cortical wall of the adjacent femoral shaft, for example with bone screws. This type of assembly is often selected when a femoral neck fracture is a part of a more complicated fracture pattern including also one or more fractures in the metaphyseal and/or diaphyseal regions of the femur. Clearly, the surgeon desires to be able to select the appropriate length of the side plate depending upon the particular traumatic condition of the patient's femur. However, the surgeon's flexibility in this regard typically requires the hospital to maintain a costly inventory of implants.